The present invention relates to a multi-layer extrusion die, and, more particularly, to the die which is used by being connected with an extruder for extruding synthetic resin (hereinafter referred to as "resin") in order to form a multi-layer sheet.
Hetherto, there are known several types of such multi-layer extrusion die. For example, Japanese Examined Patent Publication No. 1628/1974 disclosed a multi-layer extrusion die. The die is capable of forming a four-layer sheet by laying a two-layer sheet on the other two-layer sheet along a flow of resins. However, in the die there are some problems, e.g. a size of the die is large, a construction of the die is complicated and the production cost of the die is high.
Further as to a die disclosed in Japanese Examined Publication No. 6860/1975, though a structure of the die is relatively simple, an accuracy in thickness of each layer is not high. For example, the thickness of each layer is not uniform in the transverse direction.
Accordingly, there has been desired a multi-layer extrusion die which is simple in structure and capable of forming a multi-layer sheet with a high accuracy in thickness of each layer, particularly even in the transverse direction.